Nucleic acid-based tests for RhD typing, gender determination and nucleic acid quantification

ABSTRACT

The invention in part provides nucleic acid-based assays, which are particularly useful for non-invasive prenatal testing. The invention in part provides compositions and methods for RhD typing, detecting the presence of fetal nucleic in a sample, determining the relative amount of fetal nucleic acid in a sample and determining the sex of a fetus, wherein each of the assays may be performed alone or in combination.

RELATED APPLICATIONS

This patent application is a continuation of U.S. patent application Ser. No. 12/027,954 filed on Feb. 7, 2008, entitled NUCLEIC ACID-BASED TESTS FOR RHD TYPING, GENDER DETERMINATION AND NUCLEIC ACID QUANTIFICATION, naming Paul Andrew Oeth, Mathias Ehrich, and Min Seob Lee as inventors, which claims the benefit of U.S. Provisional Patent Application No. 60/888,942 filed on Feb. 8, 2007, entitled NUCLEIC ACID-BASED TESTS FOR RHD TYPING, GENDER DETERMINATION AND NUCLEIC ACID QUANTIFICATION, naming Paul Andrew Oeth and Mathias Ehrich as inventors. The entirety of each of these patent applications is incorporated herein by reference, including, without limitation, all text, tables and drawings.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted in ASCII format via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on May 12, 2008, is named SEQ-6005-UT_Seqlist.txt and is 59,263 bytes in size.

FIELD

The invention pertains generally to the field of RhD typing, which finds use, for example, in prenatal testing.

BACKGROUND

The Rh system is a highly polymorphic blood group system that plays an important role in haemolytic transfusion reactions, neonatal haemolytic disease and autoimmune haemolytic anemia. There are two different, but highly homologous, genes in the Rh system. One gene (RhD) encodes the D polypeptide, while the other gene (RHCE) encodes the CcEe polypeptide. RhD carries the D antigen—the most potent blood group immunogen. This antigen is absent from a relatively large segment (15-17%) of the population (the Rh-negative phenotype), as a result of RhD gene deletion or other RhD gene alterations (e.g., gene conversion, Pseudogene RhD psi). As used herein the term “psi” refers to the Greek symbol “ψ.” RHCE exists in four allelic forms and each allele determines the expression of two antigens in Ce, ce, cE or CE combination (RHCE is the collective name of the four alleles).

Tests for determining RhD type are critical for a wide range of applications. When blood of a rhesus D (RhD) positive donor is given to an RhD negative patient there is a high chance that alloantibody formation occurs. RhD antibodies will lead to rapid destruction of RhD-positive red cells and to transfusion reactions. Furthermore, when a woman with red cell or platelet antibodies becomes pregnant, those antibodies can cross the placenta and can destruct the red cells or the platelets of the unborn child.

In the past, nucleic acid-based RhD typing was performed on fetal nucleic acid procured through invasive means. However, conventional invasive sampling techniques that analyze fetal DNA from amniotic fluid or chorionic villus are costly and may lead to miscarriage and sensitization of the mother. An alternative source of fetal DNA was shown to be maternal plasma and serum (Lo et al., Lancet 350, 485-487 (1997)).

SUMMARY

Recent years have shown a significant increase in the efforts to use circulating cell-free fetal DNA in maternal plasma for non-invasive prenatal diagnostics for example in sex-linked disorders, fetal rhesus D status and beta-thalassaemia (Lo, Y. M. D. et al. Am. J. Hum. Genet. 62, 768-775 (1998); and Lo, Y. M. D. et al. N. Engl. J. Med. 339, 1734-1738 (1998); both of which are hereby incorporated by reference). In addition to prenatal diagnostics, circulating free fetal nucleic acid may also be used, inter alia, to determine the presence of fetal nucleic acid in a sample, to determine the amount of fetal nucleic acid in a sample, and to determine the sex of a fetus. A non-invasive RhD typing test that is sensitive and accurate enough to determine the RhD genotype of fetal DNA using maternal plasma, but also fast, reliable and affordable enough to be used for a wide range RhD-related applications (e.g., testing donor blood) can serve as an invaluable tool for prenatal diagnostics and blood-related testing.

The invention in part provides nucleic acid-based assays that are particularly useful for non-invasive prenatal testing. The invention in part provides compositions and methods for RhD typing, detecting the presence of fetal nucleic in a sample, determining the relative amount of fetal nucleic acid in a sample, and determining the sex of a fetus, wherein each of the assays may be performed alone or in combination.

The invention in part provides compositions and methods for determining RhD type. In one embodiment, the compositions and methods of the invention may be used to determine the presence or absence of one or more exons in the RhD gene. In a related embodiment, the compositions and methods of the invention may be used to determine the presence or absence of any one of exon 4, exon 5, exon 7 or exon 10 in the RhD gene. In a related embodiment, the compositions and methods of the invention may be used to determine the presence or absence of the RhD pseudogene psi. In a related embodiment, the zygosity of the pseudogene psi is also determined. In another related embodiment, the compositions and methods of the invention may be used to determine the presence or absence of exon 10 of the RhD gene, whereby the presence of exon 10 acts as a positive control for the occurrence of nucleic acid amplification. In another related embodiment, determining RhD type is carried out by annealing an extend primer to a region of the exon, and extending the primer with one or more nucleotides, chain terminating nucleotides or any combination thereof, further wherein the exon region is selected such that primer extension distinguishes between an RhD exon or RhC exon, and whereby the identity of the primer extension product confirms the presence of an RhD exon versus an RhC exon. In some embodiments, the exon region is selected such that primer extension distinguishes between an RhD exon or RhD pseudogene exon, and whereby the identity of the primer extension product confirms the presence of an RhD exon versus an RhD pseudogene exon. In a related embodiment, determining RhD type is carried out by annealing an extend primer to a region of the exon, and extending the primer with one or more nucleotides, chain terminating nucleotides or any combination thereof, further wherein the exon region is selected such that primer extension distinguishes between an RhD gene or RhD psi pseudogene, and whereby the identity of the primer extension product confirms the presence of an RhD gene versus an RhD psi pseudogene.

In certain embodiments, a probe oligonucleotide having the nucleotide sequence of an extend primer described herein, or a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical) to the sequence of an extend primer, and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon) is utilized in place of an extend primer. In such embodiments, the probe oligonucleotide includes a quenchable, detectable label, such as a fluorescent label suitable for use in quantitative polymerase chain reaction detection procedures, for example, known to the person of ordinary skill in the art. Such probe oligonucleotides can be utilized in detection procedures known to the person of ordinary skill in the art, such as quantitative polymerase chain reaction procedures (utilized in a quantitative or non-quantitative format). Quantitative polymerase chain reaction procedures often incorporate the use of a polymerase having exonuclease activity selected by the person of ordinary skill in the art.

The invention in part provides compositions and methods to analyze a nucleic acid sample for the presence or absence of one or more RhD exons, comprising the steps of amplifying the one or more RhD exons with one or more primer pairs provided in Table 3; determining the presence or absence of the amplification products from the amplification reaction, thereby determining the Rh status of an individual. In a related embodiment, the sample is blood from a pregnant female. In some embodiments, one or more of exon 4, exon 5, exon 7 or exon 10 of the RhD gene. In some embodiments, one or more of exon 4, exon 5, exon 7 or exon 10 of the RHCE gene is analyzed. In some embodiments, the exons are analyzed in a multiplexed amplification reaction. In a related embodiment, two or more multiplexed assays are performed in parallel. In some embodiments, the sample is blood, plasma or serum from a pregnant female. In a related embodiment, the sample contains fetal nucleic acid and maternal nucleic acid. In a related embodiment, the RhD status of the fetus and mother are determined in a multiplexed amplification reaction, or a combination of two or more multiplexed reactions. In a related embodiment, the primer pairs in Table 3 comprise a tag sequence to improve multiplexing. In some embodiments, the presence or absence of amplification products is determined by mass spectrometry. In some embodiments, the presence or absence of amplification products is determined by detection of hybridization of the amplification products to a gene chip. In some embodiments, the presence or absence of amplification products is determined by real time-PCR (alternatively called RT-PCR or Q-PCR).

In a related embodiment, the invention in part provides a method of analyzing a sample comprising nucleic acid to determine an Rh genotype, comprising amplifying one or more RhD gene exons or fragments thereof with one or more pairs, or combinations thereof, of amplification primers (i) comprising one of the full length nucleotide sequences hereafter, (ii) comprising one of the underlined nucleotide sequences hereafter, or (iii) comprising one of the underlined nucleotide sequences hereafter and a tag nucleotide sequence:

Exon 4 (psi zygosity) Primer Pair 1: ACGTTGGATGCTGCCAAAGCCTCTACACG (SEQ ID NO: 1) and ACGTTGGATGTGGCAGACAAACTGGGTGTC; (SEQ ID NO: 2) or Exon 4 (psi zygosity) Primer Pair 2: ACGTTGGATGAGAACGGAGGATAAAGATCAGAC (SEQ ID NO: 3) and ACGTTGGATGAGCCAGCATGGCAGACAAACTG, (SEQ ID NO: 4) and analyzing the amplification products from the first step to determine the presence or absence of one or more RhD gene exons or fragments thereof, wherein the presence or absence of one or more RhD gene exons or fragments thereof is indicative of an Rh genotype. In some embodiments, each primer of the amplification primer pair may comprise the entire sequence shown or only the underlined sequence, wherein the underlined portion of the primer is a sequence-specific primer sequence and the non-underlined portion is a tag sequence for improved multiplexing. The tag nucleotide sequence may be any tag sequence known in the art, or selected by a person of ordinary skill in the art, that improves multiplexing (e.g., improves mass spectrometry multiplexing). In some embodiments, the invention in part includes primers that are substantially similar to the primers provided herein, for example, a primer having a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical), and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon). For example, one or more bases of a primer sequence may be changed or substituted, for example with an inosine, but the primer still maintains the same specificity and plexing ability.

In a related embodiment, the invention in part provides a method of analyzing a sample comprising nucleic acid to determine an Rh genotype, comprising amplifying one or more RhD gene exons or fragments thereof with one or more pairs, or combinations thereof, of amplification primers (i) comprising one of the full length nucleotide sequences hereafter, (ii) comprising one of the underlined nucleotide sequences hereafter, or (iii) comprising one of the underlined nucleotide sequences hereafter and a tag nucleotide sequence:

Exon 4 (psi insertion) Primer Pair 1: ACGTTGGATGGACTATCAGGGCTTGCCCCG (SEQ ID NO: 5) and ACGTTGGATGTGCGAACACGTAGATGTGCA; (SEQ ID NO: 6) and analyzing the amplification products from the first step to determine the presence or absence of one or more RhD gene exons or fragments thereof, wherein the presence or absence of one or more RhD gene exons or fragments thereof is indicative of an Rh genotype. In some embodiments, each primer of the amplification primer pair may comprise the entire sequence shown or only the underlined sequence, wherein the underlined portion of the primer is a sequence-specific primer sequence and the non-underlined portion is a tag sequence for improved multiplexing. The tag sequence may be any tag sequence known in the art that improves multiplexing (e.g., multiplex analysis by mass spectrometry). In some embodiments, the invention in part includes primers that are substantially similar to the primers provided herein, for example, a primer having a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical), and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon).

In a related embodiment, the invention in part provides a method of analyzing a sample comprising nucleic acid to determine an Rh genotype, comprising amplifying one or more RhD gene exons or fragments thereof with one or more pairs, or combinations thereof, of amplification primers (i) comprising one of the full length nucleotide sequences hereafter, (ii) comprising one of the underlined nucleotide sequences hereafter, or (iii) comprising one of the underlined nucleotide sequences hereafter and a tag nucleotide sequence:

Exon 7 Primer Pair 1: (SEQ ID NO: 7) ACGTTGGATGAATCGAAAGGAAGAATGCCG and (SEQ ID NO: 8) ACGTTGGATGCTGAGATGGCTGTCACCACG; and analyzing the amplification products from the first step to determine the presence or absence of one or more RhD gene exons or fragments thereof, wherein the presence or absence of one or more RhD gene exons or fragments thereof is indicative of an Rh genotype. In some embodiments, each primer of the amplification primer pair may comprise the entire sequence shown or only the underlined sequence, wherein the underlined portion of the primer is a sequence-specific primer sequence and the non-underlined portion is a tag sequence for improved multiplexing. The tag sequence may be any tag sequence known in the art that improves multiplexing (e.g., multiplex analysis by mass spectrometry). In some embodiments, the invention in part includes primers that are substantially similar to the primers provided herein, for example, a primer having a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical), and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon).

In a related embodiment, the invention in part provides a method of analyzing a sample comprising nucleic acid to determine an Rh genotype, comprising amplifying one or more RhD gene exons or fragments thereof with one or more pairs, or combinations thereof, of amplification primers (i) comprising one of the full length nucleotide sequences hereafter, (ii) comprising one of the underlined nucleotide sequences hereafter, or (iii) comprising one of the underlined nucleotide sequences hereafter and a tag nucleotide sequence:

Exon 7 Primer Pair 1: (SEQ ID NO: 9) ACGTTGGATGAGCTCCATCATGGGCTACAA and (SEQ ID NO: 10) ACGTTGGATGTTGCCGGCTCCGACGGTATC; or Exon 7 Primer Pair 2: (SEQ ID NO: 11) ACGTTGGATGAGCTCCATCATGGGCTACAAC and (SEQ ID NO: 10) ACGTTGGATGTTGCCGGCTCCGACGGTATC, and analyzing the amplification products from the first step to determine the presence or absence of one or more RhD gene exons or fragments thereof, wherein the presence or absence of one or more RhD gene exons or fragments thereof is indicative of an Rh genotype. In some embodiments, each primer of the amplification primer pair may comprise the entire sequence shown or only the underlined sequence, wherein the underlined portion of the primer is a sequence-specific primer sequence and the non-underlined portion is a tag sequence for improved multiplexing. The tag sequence may be any tag sequence known in the art that improves multiplexing (e.g., multiplex analysis by mass spectrometry). In some embodiments, the invention in part includes primers that are substantially similar to the primers provided herein, for example, a primer having a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical), and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon).

In a related embodiment, the invention in part provides a method of analyzing a sample comprising nucleic acid to determine an Rh genotype, comprising amplifying one or more RhD gene exons or fragments thereof with one or more pairs, or combinations thereof, of amplification primers (i) comprising one of the full length nucleotide sequences hereafter, (ii) comprising one of the underlined nucleotide sequences hereafter, or (iii) comprising one of the underlined nucleotide sequences hereafter and a tag nucleotide sequence:

(SEQ ID NO: 12) ACGTTGGATGACGCTCATGACAGCAAAGTC and (SEQ ID NO: 13) ACGTTGGATGAACTCCATTTTCTCTGACTC; Exon 10 Primer Pair 2: (SEQ ID NO: 14) ACGTTGGATGACTCCATTTTCTCTGACTC and (SEQ ID NO: 12) ACGTTGGATGACGCTCATGACAGCAAAGTC, and analyzing the amplification products from the first step to determine the presence or absence of one or more RhD gene exons or fragments thereof, wherein the presence or absence of one or more RhD gene exons or fragments thereof is indicative of an Rh genotype. In some embodiments, each primer of the amplification primer pair may comprise the entire sequence shown or only the underlined sequence, wherein the underlined portion of the primer is a sequence-specific primer sequence and the non-underlined portion is a tag sequence for improved multiplexing. The tag sequence may be any tag sequence known in the art that improves multiplexing (e.g., multiplex analysis by mass spectrometry). In some embodiments, the invention in part includes primers that are substantially similar to the primers provided herein, for example, a primer having a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical), and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon). Primer Extension

The invention in part provides compositions and methods to analyze a nucleic acid sample for the presence of one or more RhD exons, comprising the steps of amplifying the one or more RhD exons with one or more primer pairs provided in Table 3; annealing one or more extend primers to the amplification products of first step, the extend primers provided in Table 3; performing a primer extension reaction; and analyzing the primer extension products to determine the Rh status of a fetus. The primer extension products may be analyzed using the RhD Test Interpretation Table provided in Table 1. In some embodiments, the presence or absence of primer extension products is determined by mass spectrometry. In some embodiments, the presence or absence of primer extension products is determined by any method known in the art.

In a related embodiment, the invention in part provides a method of analyzing a sample comprising nucleic acid to determine an Rh genotype, comprising the steps of amplifying one or more RhD gene exons or fragments thereof with one or more pairs of amplification primers (i) comprising one of the full length nucleotide sequences hereafter, (ii) comprising one of the underlined nucleotide sequences hereafter, or (iii) comprising one of the underlined nucleotide sequences hereafter and a tag nucleotide sequence:

(SEQ ID NO: 1) ACGTTGGATGCTGCCAAAGCCTCTACACG and (SEQ ID NO: 2) ACGTTGGATGTGGCAGACAAACTGGGTGTC; or Exon 4 (psi zygosity) Primer Pair 2: (SEQ ID NO: 3) ACGTTGGATGAGAACGGAGGATAAAGATCAGAC and (SEQ ID NO: 4) ACGTTGGATGAGCCAGCATGGCAGACAAACTG; annealing one or more extend primers to the amplification products from the first step, the extend primer comprising:

(SEQ ID NO: 15) gGTCTCCAATGTTCGCGCAGGCAC, or (SEQ ID NO: 16) gGATAAAGATCAGACAGCAAC; extending the primer with one or more nucleotides; and analyzing the primer extension products to determine the presence or absence of one or more RhD gene exons or fragments thereof, wherein the presence or absence of one or more RhD gene exons or fragments thereof is indicative of an Rh genotype. In some embodiments, each primer of the amplification primer pair may comprise the entire sequence shown or only the underlined sequence, wherein the underlined portion of the primer is a sequence-specific primer sequence and the non-underlined portion is a tag sequence for improved multiplexing. The tag sequence may be any tag sequence known in the art that improves multiplexing (e.g., multiplex analysis by mass spectrometry). In some embodiments, the invention in part includes primers that are substantially similar to the amplification and extend primers provided herein, for example, a primer having a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical), and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon). For example, one or more bases of a primer sequence may be changed or substituted, for example with an inosine, but the primer still maintains the same specificity and plexing ability.

In a related embodiment, the invention in part provides a method of analyzing a sample comprising nucleic acid to determine an Rh genotype, comprising the steps of amplifying one or more RhD gene exons or fragments thereof with one or more pairs of amplification primers (i) comprising one of the full length nucleotide sequences hereafter, (ii) comprising one of the underlined nucleotide sequences hereafter, or (iii) comprising one of the underlined nucleotide sequences hereafter and a tag nucleotide sequence:

(SEQ ID NO: 5) ACGTTGGATGGACTATCAGGGCTTGCCCCG and (SEQ ID NO: 6) ACGTTGGATGTGCGAACACGTAGATGTGCA; annealing one or more extend primers to the amplification products from the first step, the extend primer comprising:

(SEQ ID NO: 17) GAACGGAGGATAAAGATCAGA, or (SEQ ID NO: 18) cTGCAGACAGACTACCACATGAAC; extending the primer with one or more nucleotides; and analyzing the primer extension products to determine the presence or absence of one or more RhD gene exons or fragments thereof, wherein the presence or absence of one or more RhD gene exons or fragments thereof is indicative of an Rh genotype. In some embodiments, each primer of the amplification primer pair may comprise the entire sequence shown or only the underlined sequence, wherein the underlined portion of the primer is a sequence-specific primer sequence and the non-underlined portion is a tag sequence for improved multiplexing. The tag sequence may be any tag sequence known in the art that improves multiplexing (e.g., multiplex analysis by mass spectrometry). In some embodiments, the invention in part includes primers that are substantially similar to the amplification and extend primers provided herein, for example, a primer having a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical), and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon).

In a related embodiment, the invention in part provides a method of analyzing a sample comprising nucleic acid to determine an Rh genotype, comprising the steps of amplifying one or more RhD gene exons or fragments thereof with one or more pairs of amplification primers (i) comprising one of the full length nucleotide sequences hereafter, (ii) comprising one of the underlined nucleotide sequences hereafter, or (iii) comprising one of the underlined nucleotide sequences hereafter and a tag nucleotide sequence:

(SEQ ID NO: 7) ACGTTGGATGAATCGAAAGGAAGAATGCCG and (SEQ ID NO: 8) ACGTTGGATGCTGAGATGGCTGTCACCACG; annealing one or more extend primers to the amplification products from the first step, the extend primer comprising:

(SEQ ID NO: 19) ATGCCGTGTTCAACACCTACTATGCT, (SEQ ID NO: 20) GATGGCTGTCACCACGCTGACTGCTA, or (SEQ ID NO: 21) tTGTCACCACGCTGACTGCTA; extending the primer with one or more nucleotides; and analyzing the primer extension products to determine the presence or absence of one or more RhD gene exons or fragments thereof, wherein the presence or absence of one or more RhD gene exons or fragments thereof is indicative of an Rh genotype. In some embodiments, each primer of the amplification primer pair may comprise the entire sequence shown or only the underlined sequence, wherein the underlined portion of the primer is a sequence-specific primer sequence and the non-underlined portion is a tag sequence for improved multiplexing. The tag sequence may be any tag sequence known in the art that improves multiplexing (e.g., multiplex analysis by mass spectrometry). In some embodiments, the invention in part includes primers that are substantially similar to the amplification and extend primers provided herein, for example, a primer having a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical), and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon).

In a related embodiment, the invention in part provides a method of analyzing a sample comprising nucleic acid to determine an Rh genotype, comprising the steps of amplifying one or more RhD gene exons or fragments thereof with one or more pairs of amplification primers (i) comprising one of the full length nucleotide sequences hereafter, (ii) comprising one of the underlined nucleotide sequences hereafter, or (iii) comprising one of the underlined nucleotide sequences hereafter and a tag nucleotide sequence:

(SEQ ID NO: 9) ACGTTGGATGAGCTCCATCATGGGCTACAA and (SEQ ID NO: 10) ACGTTGGATGTTGCCGGCTCCGACGGTATC; or Exon 7 Primer Pair 2: (SEQ ID NO: 11) ACGTTGGATGAGCTCCATCATGGGCTACAAC and (SEQ ID NO: 12) ACGTTGGATGTTGCCGGCTCCGACGGTATC; annealing one or more extend primers to the amplification products from the first step, the extend primer comprising:

(SEQ ID NO: 22) CTTGCTGGGTCTGCTTGGAGAGATCA; extending the primer with one or more nucleotides; and analyzing the primer extension products to determine the presence or absence of one or more RhD gene exons or fragments thereof, wherein the presence or absence of one or more RhD gene exons or fragments thereof is indicative of an Rh genotype. In some embodiments, each primer of the amplification primer pair may comprise the entire sequence shown or only the underlined sequence, wherein the underlined portion of the primer is a sequence-specific primer sequence and the non-underlined portion is a tag sequence for improved multiplexing. The tag sequence may be any tag sequence known in the art that improves multiplexing (e.g., multiplex analysis by mass spectrometry). In some embodiments, the invention in part includes primers that are substantially similar to the amplification and extend primers provided herein, for example, a primer having a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical), and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon).

In a related embodiment, the invention in part provides a method of analyzing a sample comprising nucleic acid to determine an Rh genotype, comprising the steps of amplifying one or more RhD gene exons or fragments thereof with one or more pairs of amplification primers (i) comprising one of the full length nucleotide sequences hereafter, (ii) comprising one of the underlined nucleotide sequences hereafter, or (iii) comprising one of the underlined nucleotide sequences hereafter and a tag nucleotide sequence:

(SEQ ID NO: 12) ACGTTGGATGACGCTCATGACAGCAAAGTC and (SEQ ID NO: 13) ACGTTGGATGAACTCCATTTTCTCTGACTC; Exon 10 Primer Pair 2: (SEQ ID NO: 14) ACGTTGGATGACTCCATTTTCTCTGACTC and (SEQ ID NO: 12) ACGTTGGATGACGCTCATGACAGCAAAGTC; annealing one or more extend primers to the amplification products from the first step, the extend primer comprising:

(SEQ ID NO: 15) gGTCTCCAATGTTCGCGCAGGCAC; extending the primer with one or more nucleotides; and analyzing the primer extension products to determine the presence or absence of one or more RhD gene exons or fragments thereof, wherein the presence or absence of one or more RhD gene exons or fragments thereof is indicative of an Rh genotype. In some embodiments, each primer of the amplification primer pair may comprise the entire sequence shown or only the underlined sequence, wherein the underlined portion of the primer is a sequence-specific primer sequence and the non-underlined portion is a tag sequence for improved multiplexing. The tag sequence may be any tag sequence known in the art that enables multiplexing. In some embodiments, the invention in part includes primers that are substantially similar to the amplification and extend primers provided herein, for example, a primer having a nucleotide sequence that is about 90% or more identical (e.g., about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% or more identical), and further wherein the primer still is specific for a given Rh exon (i.e., specifically hybridizes to a Rh exon).

In another related embodiment, the invention in part provides a method of analyzing a sample derived from a pregnant female for the presence of one or more of exon 4, exon 5, exon 7 or exon 10 of the RhD gene from fetal nucleic acid, and exon 10 of the RhD gene from maternal nucleic acid, comprising the steps of amplifying the RhD nucleic acid with one or more primer pairs provided in Table 3; determining the presence or absence of the amplification products from the first step, thereby determining the Rh status of a fetus. In an optional embodiment, the presence or absence of exon 10 of the RhD gene may serve as a positive control for the occurrence of nucleic acid amplification or a primer extension reaction. In another related embodiment, a primer extension reaction is performed to determine the presence or absence of one or more of exon 4, exon 5, exon 7 or exon 10 of the RhD gene from fetal nucleic acid, and exon 10 of the RhD gene from maternal nucleic acid, wherein the extend primers are provided in Table 3.

The amplification products and/or primer extension products may be detected by any detection method known in the art, which includes but is not limited to RT-PCR, mass spectrometry and hybridization to a gene chip.

In one embodiment, the primer extension reaction includes the incorporation of a chain terminating nucleotide. In a related embodiment, the chain terminating nucleotide is a dideoxynucleotide, dideoxybromouridine or acyclonucleotide. In some embodiments, the extension reaction comprises incorporation of a deoxynucleotide, a dideoxynucleotide or a combination thereof. In some embodiments, the extension reaction comprises incorporation of a labeled nucleotide. In a related embodiment, the extension reaction comprises using a mixture of labeled and unlabeled nucleotides. In another related embodiment, the labeled nucleotide is labeled with a molecule selected from the group consisting of radioactive molecule, fluorescent molecule, mass label, antibody, antibody fragment, hapten, carbohydrate, biotin, derivative of biotin, phosphorescent moiety, luminescent moiety, electrochemiluminescent moiety, chromatic moiety, and moiety having a detectable electron spin resonance, electrical capacitance, dielectric constant and electrical conductivity. In another related embodiment, the labeled nucleotide is labeled with a fluorescent molecule.

The invention in part provides compositions and methods to detect the presence or absence of a target nucleic acid in a sample. In one embodiment, the compositions and methods of the invention may be used to detect the presence or absence of fetal nucleic acid in a maternal sample. In one embodiment, compositions and methods are provided for analyzing a plurality of polymorphisms in a nucleic acid sample of fetal origin; and analyzing a plurality of polymorphisms in a nucleic acid sample of maternal origin, whereby the presence of at least one polymorphism in the nucleic acid sample of fetal origin, which is not present in the nucleic acid sample of maternal origin, confirms the presence of fetal nucleic acid in the fetal nucleic acid sample. In a related embodiment, the presence of at least one polymorphism in the nucleic acid sample of fetal origin, which is not present in the nucleic acid sample of maternal origin, is a paternally-inherited allele. In some embodiments, the same polymorphisms are analyzed in fetal nucleic acid and maternal nucleic acid. In some embodiments, the polymorphism is heterozygous. The plurality of polymorphisms may include 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 or more polymorphisms. In a related embodiment, the polymorphism is a single nucleotide polymorphism (SNP), insertion/deletion, short tandem repeats (STRs), RFLPs or any other alternate form of a gene, genomic DNA or non-coding region of DNA that occupies the same position on a chromosome. The polymorphism may be naturally-occurring or synthetic. Synthetic polymorphisms may include alternative forms introduced on a synthetic oligonucleotide that serve as a competitor or control.

In a related embodiment, the invention in part provides compositions and methods of determining the presence or absence of fetal nucleic acid in the sample using the fetal identifiers set forth in Table 3 or 4. In one embodiment, the method of detecting the presence or absence of fetal nucleic acid in a sample comprises obtaining or possessing a nucleic acid sample known to be of maternal origin and suspected of comprising fetal nucleic acid; analyzing the nucleic acid sample to determine the maternal genotype of at one or more nucleotide polymorphisms selected from the group consisting of the polymorphisms set forth in Table 3 or 4; and analyzing the nucleic acid sample to determine the fetal genotype of one or more nucleotide polymorphisms selected from the group consisting of the polymorphisms set forth in Table 3 or 4, wherein a fetal genotype possessing a paternally-inherited allele indicates the presence of fetal nucleic acid. In a related embodiment, the maternal genotypes are determined from DNA that is substantially free of fetal nucleic acid. For example, in the case when the sample is blood, the maternal genotypes may be determined from the portion of the blood that comprises nucleated maternal cells (e.g., white blood cells). In one embodiment, the DNA that is substantially free of fetal nucleic acid is from peripheral blood mononuclear cells. In some embodiments, the amount of fetal DNA is determined by comparing the relative amount of paternally-inherited alleles to maternally-inherited alleles in fetal nucleic acid.

In certain embodiments, the compositions and methods of the invention may be used to detect the presence or absence of the Y-chromosome in a maternal sample, which may be used to determine the sex of a fetus. The presence or absence of the Y-chromosome in a maternal sample may be determined by performing the SRY assay provided herein. The SRY assay is a highly sensitive quantitative internal standard assay that detects trace amounts of the Y-chromosome.

The presence or absence of the Y-chromosome in a maternal sample may also be determined by performing the AMG assay provided herein. The presence or absence of a target nucleic acid may be determined in combination with other assays, such as an RhD assay or sex test assay. The methods may also be used for other applications, including but not limited to, paternity testing, forensics or quality control assays.

The invention in part also provides compositions and methods to determine the relative amount of target nucleic acid in a sample (e.g., fetal nucleic acid in a pregnant female sample). In one embodiment, the compositions and methods of the invention may be used to quantitate the relative amount of the alleles at a heterozygous polymorphic site, wherein said heterozygous polymorphic site has been identified by determining the sequence of alleles at a polymorphic site from template DNA obtained from a maternal sample, wherein said relative amount is expressed as a ratio, wherein said ratio indicates the relative amount of fetal nucleic acid present in the maternal sample. In a related embodiment, the polymorphic sites are provided in Table 3 or 4, 3 or 4. In some embodiments, the polymorphic site is an insertion/deletion, STR or RFLP.

In a related embodiment, the invention in part provides compositions and methods to determine the relative amount of fetal DNA in a sample (e.g., plasma of a pregnant woman carrying a male fetus), which comprises annealing one or more X and Y-specific AMG sequences to the fetal DNA, the primers provided in FIG. 3A-3C; performing a primer extension reaction; and analyzing the primer extension products to determine the ratio of the X and Y-specific extension products. In a related embodiment, the fetal AMG amplicon is first amplified using the amplification primers provided in FIGS. 3A-3C. In another related embodiment, the competitors provided in FIGS. 3A-3C are introduced as an internal standard to determine copy number.

In a related embodiment, the invention in part provides compositions and methods to determine the relative amount of target nucleic acid in a sample (e.g., fetal nucleic acid in plasma of a pregnant woman carrying a male fetus). In one embodiment, one or more Y-specific SRY sequences are annealed to the fetal DNA, the primer comprising GTTACCCGATTGTCCTAC (SEQ ID NO: 23); performing a primer extension reaction; and analyzing the primer extension products to determine the presence and relative amount of Y-specific extension products. In a related embodiment, the fetal SRY amplicon is first amplified using the following amplification primer pair:

(SEQ ID NO: 24) ACGTTGGATGAGCATCTAGGTAGGTCTTTG and (SEQ ID NO: 25) ACGTTGGATGAGCAACGGGACCGCTACAG.

In some embodiments, the total copy number of nucleic acid molecules for the human serum albumin (ALB) gene is determined. Methods for determining the total copy number of nucleic acid present in a sample comprise detecting albumin-specific extension products and comparing the relative amount of the extension products to competitors introduced to the sample. In a related embodiment, the invention in part provides compositions and methods to determine the relative amount of fetal DNA in a sample (e.g., plasma of a pregnant woman carrying a male fetus), which comprises annealing one or more albumin gene sequences to the fetal DNA, the primers provided in FIG. 4; performing a primer extension reaction; and analyzing the primer extension products to determine the relative amount of ALB extension products. In a related embodiment, the fetal ALB amplicon is first amplified using the amplification primers provided in FIG. 4. The assay is useful to measure how much nucleic acid (e.g., total copy number) is present in a sample or loaded into a particular reaction. The assay may serve as an internal control and a guide to the likelihood of success for a particular PCR reaction. For example, if only 400 copies of ALB are measured then the probability of detecting any fetal DNA may be considered low. In another related embodiment, the competitors provided in FIG. 4 are introduced as an internal standard to determine copy number. In one embodiment, 200, 300, 400, 500, 600, 700, 800 or more competitors are introduced to the assay.

The methods of the present invention may be performed alone or in combination with other tests.

In one embodiment the sample is blood. In certain embodiments, the sample is blood from a pregnant female. In a related embodiment, the blood is obtained from a human pregnant female when the fetus is at a gestational age selected from the group consisting of: 0-4, 4-8, 8-12, 12-16, 16-20, 20-24, 24-28, 28-32, 32-36, 36-40, 40-44, 44-48, 48-52, and more than 52 weeks. In another related embodiment, the sample is obtained through non-invasive means. In some embodiments, the nucleic acid is obtained from plasma from said blood. In some embodiments, the nucleic acid is obtained from serum from said blood. In some embodiments, the sample comprises a mixture of maternal DNA and fetal DNA. While the invention is not limited by how the sample is obtained, the methods and compositions of the invention are particularly useful for assaying samples obtained by non-invasive means, which may contain lower amounts of nucleic acid to be assayed. In a related embodiment, the sample is processed to selectively enrich fetal nucleic acid. In another related embodiment, the maternal and fetal Rh genotypes are determined in a multiplexed assay, or a combination of two or more multiplexed reactions. In a further related embodiment, the maternal Rh genotype is determined by analyzing maternal nucleic acid from maternal nucleated cells, for example, peripheral mononuclear blood cells (PMBC).

The invention in part utilizes multiplexed reactions to improve throughput and reduce cost. Thus, provided herein are optimized methods for performing a primer mass extension assay, including an optimized PCR amplification reaction that produces amplified targets for subsequent multiplexed primer mass extension genotyping analysis using mass spectrometry. Also provided herein are optimized methods for performing multiplexed amplification reactions and multiplexed primer mass extension reactions in a single well to further increase the throughput and reduce the cost per genotype for primer mass extension reactions. The nucleic acid target-region amplification and primer mass extension genotyping reactions have been optimized herein to permit moderate to high level multiplexing reactions with greater efficiency and accuracy, while at the same time not adversely affecting the mass spectrometry analysis of mass extension products.

In one embodiment, the amplification primers provided in Table 3 comprises a 5′ tag and a gene-specific sequence (underlined). The tag is used to assist in the amplification of the nucleic acids. The primer tags may serve to stabilize the primer during amplification or they may serve as universal primer sites. More specifically, once the RhD gene nucleic acids have been PCR amplified using the primers, primers to the tags are used to further amplify the sequences. In one embodiment, both amplification steps are performed simultaneously. As will be appreciated by those skilled in the art, primers without the 5′ tag (primer sequences underlined in the Table) can be used in the method of the invention in order to amplify the RhD gene nucleic acids. Alternatively, the primer sequences can comprise different tag sequences than the tags indicated in the Table. Tag sequences useful for multiplex amplification reactions are well known in the art.

In some embodiments, the amplification primers allow for sequence specific amplification. For example, the PCR primers are designed to discriminate against amplification of the RHCE gene by taking advantage of sequence differences between the RHD and RHCE gene. In some embodiments, the extend primer of the post-PCR primer extension reaction is designed to target a sequence difference between RHD and RHCE gene so that any leakage in the allele-specific amplification would lead to a distinguishable primer extension product that does not interfere with correct interpretation of RHD detection.

In particular embodiments, a sequence tag is attached to a plurality of primary and secondary primer pairs provided in Table 3. The sequence tag can be attached to either one or both of the primary and secondary primers from each pair. Typically, the sequence tag is attached to the primary and secondary primer of each pair. The sequence tags used herein can range from 5 up to 20, from 5 up to 30, from 5 up to 40, or from 5 up to 50 nucleotides in length, with a sequence tag of 10-mer length being particularly useful in the methods provided herein. The sequence tag need not be the same sequence for each primer pair in the multiplexed amplification reaction, nor the same sequence for a primary and secondary primer within a particular amplification pair. In a particular embodiment, the sequence tag is the same for each primer in the multiplexed amplification reaction. For example, in certain embodiments, the sequence tag is a 10-mer, such as -ACGTTGGATG- (SEQ ID NO: 26), and is attached to the 5′ end of each primary and secondary primer. In particular embodiments of the methods provided herein, only a single primer pair is used to amplify each particular nucleic acid target-region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-1F provide the location design of the RhD primers. The amplification primers are highlighted and the extend primers are in bold. The Figures also provide the extend primer product associated with each respective assay result. For example, in FIG. 1A, an extension product with an adenine (A) chain terminating nucleotide indicates the presence of exon 4 of the RhD gene, an extension product with an adenine and a thymine (A & T) chain terminating nucleotide indicates the presence of exon 4 of the RhD psi pseudogene, and an extension product with a cytosine (C) chain terminating nucleotide indicates the presence of exon 4 of the RHCE gene. FIG. 1A discloses SEQ ID NOS 5-6, 18 and 174-176, respectively, in order of appearance. FIG. 1B discloses SEQ ID NOS 3-4, 177 and 174-175, respectively, in order of appearance. FIG. 1C discloses SEQ ID NOS 7-8, 19-20 and 178-179, respectively, in order of appearance. FIG. 1D discloses SEQ ID NOS 180-184, respectively, in order of appearance. FIG. 1E discloses SEQ ID NOS 11, 10 and 185-187, respectively, in order of appearance. FIG. 1F discloses SEQ ID NOS 12-13 and 188-190, respectively, in order of appearance.

FIG. 2 provides the location design of the SRY primers in the SRY gene coding sequence (SEQ ID NO: 191). The amplification primers are highlighted and the extend primers are underlined. Where the PCR primers are provided alone, the sequence-specific portion of the primer is underlined, and the multiplex tag is not underlined. In addition, competitor sequences are provided. FIG. 2 discloses SEQ ID NOS 192-201, 25, 24, 202-212, respectively, in order of appearance.

FIG. 3A-3C provide the location design of the AMG primers. The amplification primers are underlined once and the extend primers are underlined twice. In addition, competitor sequences are provided. FIG. 3C includes a Results Table that shows the different masses generated by each of the AMG and SRY assays, which may be used to interpret the results from the assays. FIG. 3A discloses SEQ ID NOS 213-221, respectively, in order of appearance. FIG. 3B discloses SEQ ID NOS 213-214 and 222-226, respectively, in order of appearance. FIG. 3C discloses SEQ ID NOS 213-241, 227-228, 217, 229-231, 217, 230, 232-233, 194 and 234, respectively, in order of appearance.

FIG. 4 provides the location design of the albumin (ALB) primers. The amplification primers are highlighted and the extend primer is underlined twice. Where the PCR primers are provided alone, the sequence-specific portion of the primer is underlined, and the multiplex tag is not underlined. In addition, competitor sequences are provided. FIG. 4 discloses SEQ ID NOS 235-241, respectively, in order of appearance.

FIG. 5 shows the use of single nucleotide polymorphisms (SNP's) Fetal Identifiers to confirm the presence of fetal DNA by paternally-inherited alleles.

FIG. 6 shows representative mass spectra demonstrating the correlation between fetal DNA amounts estimated from AMG XY and from Fetal Identifier assays. The results were generated using the AMG primers provided in FIG. 3.

FIG. 7 depicts the validation scheme, performance criteria and model system used to qualify multiplex SNP assays for their utility in identifying the presence for fetal DNA.

FIG. 8 depicts typical performance results for a qualified fetal identifier. Here the ability of the SNP assay to estimate the quantity of fetal DNA in the background of maternal DNA was verified for a total of 1700 copies and a total of 170 copies using genomic DNA mixtures. Note that the standard deviation of the estimate of fetal DNA increases due to the significant influence of the sampling error at low copy numbers

FIG. 9 shows the performance of multiplexed SNP assays (21 assays total) for detection of paternally-inherited alleles in a model system.

FIG. 10 (provided in duplicate) shows different multiplexed assay schemes of the invention.

DETAILED DESCRIPTION

The determination of fetal Rh genotypes from maternal plasma is usually performed by PCR amplification of individual RhD exons. Negative test results, in particular for female fetuses, can require additional tests confirming the presence of sufficient amounts of fetal DNA. The compositions and methods of the invention offer nucleic acid-based tests for determining Rh type and determining the relative amount of target nucleic acid in a sample. The tests are particularly useful for prenatal diagnostics, wherein the presence and relative amount of fetal nucleic acid in a maternal sample can be determined, and further wherein fetal and maternal Rh type can be determined in a highly sensitive, accurate multiplexed reaction. The invention, therefore, provides an alternative method that further comprises high-frequency single nucleotide polymorphisms (SNPs) to determine the amount of fetal nucleic acid present in a sample, which in turn reduces the number of inconclusive tests.

The test primers were designed to ensure that the exon sequence for exons 4, 5, 7 and 10 inclusive of RhD is amplified by the RhD MPX PCR of the invention. The location design of the RhD primers is illustrated in FIGS. 1A-1F.

The assays provided herein offer many advantageous over existing RhD typing methods. Specifically, the multiplexed test reagents address the limited availability of fetal nucleic acid, complexity of genetic changes and high quality testing. The multiplexed RhD/Fetal Identifier assays allow for comprehensive non-invasive Rh genotyping of fetal DNA in only two reactions, while guarding against false-interpretation of negative test results caused by insufficient amounts of fetal DNA. Alternatively, the reactions are performed in a single, multiplexed reaction. The assays have built in quality controls to improve the accuracy of results. The RhDψ pseudogene is recognized even in heterozygote state. The SRY assay is highly sensitive and specific for paternal alleles, and the determination of maternal baseline requires only one additional reaction. Finally, the assay can be used for analysis of adult blood donor subjects. This is important in connection with subjects who receive frequent transfusions, for example, those with sickle cell anemia.

In one embodiment, the invention also relates to a method for determining whether a patient in need of a blood transfusion is to be transfused with RhD negative blood from a donor. The invention has important implications for devising a transfusion therapy in humans. For example, it can now be conveniently tested whether the patient actually needs a transfusion with a RhD negative blood or whether such precautions need not be taken.

As used herein, “sample” refers to a composition containing a material to be detected or analyzed. Samples include “biological samples”, which refer to any material obtained from a living source, for example, an animal such as a human or other mammal, a plant, a bacterium, a fungus, a protist or a virus or a processed form, such as amplified or isolated material. The sample may be obtained through invasive (e.g., amniocentesis) or non-invasive (e.g., blood draw) means. In a preferred embodiment, the sample is obtained non-invasively. The biological sample can be in any form, including a solid material such as a tissue, cells, a cell pellet, a cell extract, a biopsy, or feces, or a biological fluid such as urine, whole blood, plasma, serum, interstitial fluid, vaginal swab, pap smear, peritoneal fluid, lymph fluid, ascites, sweat, saliva, follicular fluid, breast milk, non-milk breast secretions, cerebral spinal fluid, seminal fluid, lung sputum, amniotic fluid, exudate from a region of infection or inflammation, a mouth wash containing buccal cells, synovial fluid, or any other fluid sample produced by the subject. In addition, the sample can be solid samples of tissues or organs, such as collected tissues, including bone marrow, epithelium, stomach, prostate, kidney, bladder, breast, colon, lung, pancreas, endometrium, neuron, muscle, and other tissues. Samples can include organs, and pathological samples such as a formalin-fixed sample embedded in paraffin. If desired, solid materials can be mixed with a fluid or purified or amplified or otherwise treated. Samples examined using the methods described herein can be treated in one or more purification steps in order to increase the purity of the desired cells or nucleic acid in the sample. Samples also can be examined using the methods described herein without any purification steps to increase the purity or relative concentration of desired cells or nucleic acid. As used herein, the term “blood” encompasses whole blood or any fractions of blood, such as serum and plasma as conventionally defined.

The terms “nucleic acid” and “nucleic acid molecule” may be used interchangeably throughout the disclosure. The terms refer to a deoxyribonucleotide (DNA), ribonucleotide polymer (RNA), RNA/DNA hybrids and polyamide nucleic acids (PNAs) in either single- or double-stranded form, and unless otherwise limited, would encompass known analogs of natural nucleotides that can function in a similar manner as naturally occurring nucleotides.

As used herein, the term “amplifying” or “amplification” refers to means for increasing the amount of a biopolymer, especially nucleic acids. Based on the 5′ and 3′ primers that are chosen, amplification also serves to restrict and define a target-region or locus of the genome which is subject to analysis. Amplification can be by any means known to those skilled in the art, and in particular embodiments, includes the use of the polymerase chain reaction (PCR). The phrase simultaneous amplification refers to the amplification of 2 or more nucleic acid target-regions at the same time. The simultaneous amplification is typically within the same amplification mixture.

As used herein, the term “multiplexing” refers to the simultaneous amplification or primer mass extension reaction of more than one oligonucleotide or primer (e.g., in a single reaction container); or the simultaneous analysis of more than one oligonucleotide, in a single mass spectrometric or other mass measurement, i.e., a single mass spectrum or other method of reading sequence.

As used herein, the phrase “simultaneous amplification” refers to the multiplexed amplification of 2 or more loci or nucleic acid target-regions in a single reaction mixture. Simultaneous amplification therefore encompasses 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, 15 or more, 16 or more, 17 or more, 18 or more, 19 or more, 20 or more, 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, 80 or more, 100 or more, 200 or more, 500 or more, 1000 or more, 2000 or more amplification reactions. The amplification of each particular target-region occurs in parallel at the same time. Although it is contemplated herein that the simultaneous amplifications can occur in separate reaction mixtures, for the methods provided herein the simultaneous amplification reactions typically occur in the same single reaction. Likewise multiplexed primer mass extension refers to the simultaneous extension of 2 or more genotyping primers in a single reaction mixture. Accordingly, multiplexed primer mass extension therefore encompasses [5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, 15 or more, 16 or more, 17 or more, 18 or more, 19 or more, 20 or more, 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, 80 or more, 100 or more, 200 or more, 500 or more, 1000 or more, 2000 or more primer mass extension reactions. Multiplexed amplification and primer mass extension reactions also encompass 21, 22, 23, 24, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 100, 1000 or more reactions.

As used herein, the phrase “target nucleic acid” refers to one or more nucleic acids, such as genomic DNA, from which one or more regions or loci are to be amplified.

As used herein, the phrase “nucleic acid-target region” refers to the region-specific areas or loci of a target nucleic acid (e.g., UTR, exon or intron) that are amplified for subsequent sequence variation analysis. The amplified nucleic acid-target regions each contain at least one sequence variation or site that is being genotyped.

As used herein, the term “polymorphism” refers to the coexistence of more than one form or allele of a nucleic acid, such as a chromosome, or portion thereof. For example, a portion or locus of a gene at which there are at least two different alleles, i.e., two different nucleotide sequences, is referred to as a polymorphic loci, site or region of a gene. A polymorphic loci can be a single nucleotide (e.g., SNP) or can be several nucleotides in length (e.g., insertions or deletions). Accordingly, polymorphism includes substitutions, insertions, duplications and deletions of nucleotides. A polymorphism can also refer to a particular nucleotide(s) or nucleotide sequence occurring at a particular polymorphic site.

As used herein, the term “genotyping” refers to the process of determining the particular nucleotide or nucleotides (e.g., sequence variation) either present or absent at a particular polymorphic loci or genomic location.

As used herein, “allele”, which is used interchangeably herein with “allelic variant” refers to alternative forms of a nucleic acid such as a gene or polymorphic regions thereof. Alleles occupy the same locus or position (referred to herein as a polymorphic region) on homologous chromosomes. When a subject has two identical alleles of a polymorphic region within a gene, the subject is said to be homozygous for the allele. When a subject has two different alleles of a polymorphic region within a gene, the subject is said to be heterozygous for the allele. Alleles of a specific gene can differ from each other at a polymorphic region corresponding to a single nucleotide, or several nucleotides, and can include substitutions, deletions, insertions and duplications of nucleotides. An allele of a gene can also be a form of a gene containing a mutation.

As used herein, the term “non-homologous variant” refers to one or more sequence variations that exist between two or more highly homologous genes (e.g., RhD and RHCE), pseudogenes, transcript variants, repeats or other similar genomic sequences. Non-homologous variants between genes can differ from each other by a single nucleotide, or several nucleotides, and can include substitutions, deletions, insertions and duplications of nucleotides. For example, an RhD pseudogene exists that contains a 37 base pair insertion in exon 4. In the context of the present invention, the 37 base pair insertion of the pseudogene is considered a non-homologous variant. Non-homologous variants usually occupy the same locus or position on highly homologous genes (e.g., in the same, corresponding exon or intron). For example, sequence variations between the highly homologous RhD and RHCE genes are particularly useful for RhD testing.

As used herein, the term “genotype” refers to the identity of the alleles or non-homologous variants present in an individual or sample. The term “genotyping a sample” or “genotyping an individual” refers to determining a specific allele or specific nucleotide(s) in a sample or carried by an individual at particular region(s).

As used herein, the phrase “RhD testing” refers to a DNA-based genotyping method to detect the RhD and/or RHCE genes and their prevalent alleles, non-homologous variants and combinations thereof (e.g., RhD sequence that contains replacements with homologous RHCE sequences). RhD testing may be used to determine an RhD phenotype.

As used herein, the term “Rh phenotype” refers to determining the presence or absence of antigens of the Rh blood group, specifically red cell antigens C, D and E. An individual is either Rh-positive or Rh-negative for a given antigen. For example, “an RhD-negative” individual does not express antigen D, whereas an RhD-positive individual does express antigen D. “Rh incompatibility” occurs when red cells from a Rhesus positive fetus cross the placenta and sensitize a Rhesus negative mother, especially at parturition. The mother's antibody may then, in a subsequent pregnancy, cause haemolytic disease of the newborn if the fetus is Rhesus positive.

Whether detecting sequence differences, detecting amplification products or primer extension products, any detection method known in the art may be utilized. While many detection methods include a process in which a DNA region carrying the polymorphic site of interest is amplified, ultra sensitive detection methods which do not require amplification may be utilized in the detection method, thereby eliminating the amplification process. Polymorphism detection methods known in the art include, for example, primer extension or microsequencing methods, ligase sequence determination methods (e.g., U.S. Pat. Nos. 5,679,524 and 5,952,174, and WO 01/27326), mismatch sequence determination methods (e.g., U.S. Pat. Nos. 5,851,770; 5,958,692; 6,110,684; and 6,183,958), microarray sequence determination methods, restriction fragment length polymorphism (RFLP) procedures, PCR-based assays (e.g., TAQMAN® PCR System (Applied Biosystems)), nucleotide sequencing methods, hybridization methods, conventional dot blot analyses, single strand conformational polymorphism analysis (SSCP, e.g., U.S. Pat. Nos. 5,891,625 and 6,013,499; Orita et al., Proc. Natl. Acad. Sci. U.S.A 86: 27776-2770 (1989)), denaturing gradient gel electrophoresis (DGGE), heteroduplex analysis, mismatch cleavage detection, and techniques described in Sheffield et al., Proc. Natl. Acad. Sci. USA 49: 699-706 (1991), White et al., Genomics 12: 301-306 (1992), Grompe et al., Proc. Natl. Acad. Sci. USA 86: 5855-5892 (1989), and Grompe, Nature Genetics 5: 111-117 (1993), detection by mass spectrometry (e.g., US 20050079521, which is hereby incorporated by reference), real time-PCR (e.g., U.S. Pat. No. 5,210,015, U.S. Pat. No. 5,487,972, both of which are hereby incorporated by reference), or hybridization with a suitable nucleic acid primer specific for the sequence to be detected. Suitable nucleic acid primers can be provided in a format such as a gene chip.

Primer extension polymorphism detection methods, also referred to herein as “microsequencing” methods, typically are carried out by hybridizing a complementary oligonucleotide to a nucleic acid carrying the polymorphic site. In these methods, the oligonucleotide typically hybridizes adjacent to the polymorphic site. As used herein, the term “adjacent” refers to the 3′ end of the extension oligonucleotide being sometimes 1 nucleotide from the 5′ end of the polymorphic site, often 2 or 3, and at times 4, 5, 6, 7, 8, 9, or 10 nucleotides from the 5′ end of the polymorphic site, in the nucleic acid when the extension oligonucleotide is hybridized to the nucleic acid. The extension oligonucleotide then is extended by one or more nucleotides, often 1, 2, or 3 nucleotides, and the number and/or type of nucleotides that are added to the extension oligonucleotide determine which polymorphic variant or variants are present. Oligonucleotide extension methods are disclosed, for example, in U.S. Pat. Nos. 4,656,127; 4,851,331; 5,679,524; 5,834,189; 5,876,934; 5,908,755; 5,912,118; 5,976,802; 5,981,186; 6,004,744; 6,013,431; 6,017,702; 6,046,005; 6,087,095; 6,210,891; and WO 01/20039. The extension products can be detected in any manner, such as by fluorescence methods (see, e.g., Chen & Kwok, Nucleic Acids Research 25: 347-353 (1997) and Chen et al., Proc. Natl. Acad. Sci. USA 94/20: 10756-10761 (1997)) and by mass spectrometric methods (e.g., MALDI-TOF mass spectrometry or electrospray mass spectrometry). Oligonucleotide extension methods using mass spectrometry are described, for example, in U.S. Pat. Nos. 5,547,835; 5,605,798; 5,691,141; 5,849,542; 5,869,242; 5,928,906; 6,043,031; 6,194,144; and 6,258,538.

Microsequencing detection methods often incorporate an amplification process that proceeds the extension step. The amplification process typically amplifies a region from a nucleic acid sample that comprises the polymorphic site. Amplification can be carried out by utilizing a pair of oligonucleotide primers in a polymerase chain reaction (PCR), in which one oligonucleotide primer typically is complementary to a region 3′ of the polymorphism and the other typically is complementary to a region 5′ of the polymorphism. A PCR primer pair may be used in methods disclosed in U.S. Pat. Nos. 4,683,195; 4,683,202, 4,965,188; 5,656,493; 5,998,143; 6,140,054; WO 01/27327; and WO 01/27329 for example. PCR primer pairs may also be used in any commercially available machines that perform PCR, such as any of the GENEAMP® Systems available from Applied Biosystems.

A microarray can be utilized for determining whether a polymorphic variant is present or absent in a nucleic acid sample. A microarray may include any oligonucleotides described herein, and methods for making and using oligonucleotide microarrays suitable for prognostic use are disclosed in U.S. Pat. Nos. 5,492,806; 5,525,464; 5,589,330; 5,695,940; 5,849,483; 6,018,041; 6,045,996; 6,136,541; 6,142,681; 6,156,501; 6,197,506; 6,223,127; 6,225,625; 6,229,911; 6,239,273; WO 00/52625; WO 01/25485; and WO 01/29259. The microarray typically comprises a solid support and the oligonucleotides may be linked to this solid support by covalent bonds or by non-covalent interactions. The oligonucleotides may also be linked to the solid support directly or by a spacer molecule. A microarray may comprise one or more oligonucleotides complementary to a polymorphic site within a nucleotide sequence in Tables 6, 7 or 8.

Fetal Identifiers

Cell-free fetal DNA constitutes only a minor fraction of the total DNA found in maternal plasma. The amount of fetal DNA in maternal plasma is dependent on the gestational age and is estimated at 3-6%.

Because the analysis is relying on the detection of a paternally-inherited disease-causing sequence, it is vital to be able to ascertain that the absence of the disease-causing sequence is a true diagnostic result and not caused by insufficient amount of circulating fetal DNA or even loss of the fetal DNA during sample processing.

The use of polymorphisms provide a means to confirm the presence of fetal DNA and therefore complete the analysis of negative, and otherwise inconclusive, test result in non-invasive prenatal diagnostics. The use of single nucleotide polymorphisms (SNPs), the most abundant type of polymorphism in the human genome, or insertion/deletion (Ins/Del) polymorphisms may serve as fetal identifiers to determine the presence of fetal DNA in a processed sample (Li, Y., Wenzel, F., Holzgreve, W., Hahn, S., Genotyping fetal paternally inherited SNPs by MALDI-TOF MS using cell-free fetal DNA in maternal plasma: Influence of size fractionation. Electrophoresis 27, 3889-3896 (2006); Van der Schoot, C. E., Rijnders, R. J., Bossers, B., de Haas, M., Christiaens, G. C., Dee, R. Real-time PCR of bi-allelic insertion/deletion polymorphisms can serve as a reliable positive control for cell-free fetal DNA in non-invasive prenatal genotyping [abstract] Blood 102, 93a (2003); and Chow, K. C., Chiu, R. W., Tsui, N. B., Ding, C., Lau, T. K., Leung, T. N., Lo, Y. M., Mass Spectrometric detection of a SNP panel as an internal positive control for fetal DNA analysis in maternal plasma. Clin. Chem. 53, 141-142 (2007), all of which are hereby incorporated by reference).

A SNP is considered informative for the determination of the presence of fetal DNA, if the mother is homozygous and the fetus inherited the opposite allele from the father, rendering the genotype of the fetus heterozygous.

To ensure a high probability that the presence of fetal DNA can be confirmed by the presence of the paternally-inherited allele in at least 1 SNP, a sufficient number of SNPs or Ins/Dels with a high population frequency (>0.4 for the minor frequent allele) has to be analyzed. A scheme exemplifying the concept of using SNPs to confirm the presence of fetal DNA in maternal plasma is depicted in FIG. 5.

Analysis of multiple polymorphisms in DNA extracted from maternal plasma creates a two-fold challenge: firstly, the paternally-inherited allele needs to be detected in the background of the maternal DNA; secondly, the high number of polymorphisms require significant sample material and a significant number of reactions before a conclusive test result is achieved.

Thus the invention in part provides a multiplexed panel of SNPs to establish a universal assay panel for non-invasive prenatal diagnostics.

Kits

Furthermore, the invention relates to a kit comprising the compositions of the invention. Parts of the kit can be packaged individually in vials or in combination in containers or multicontainer units. The kit of the present invention may be advantageously used for carrying out the method of the invention and could be, inter alia, employed in a variety of applications referred to above. The manufacture of the kits follows preferably standard procedures which are known to people skilled in the art.

EXAMPLES

The following examples illustrate but do not limit the invention.

Example 1 RhD Test

Analysis of RhD exons and SNPs was enabled by multiplex PCR followed by multiplexed allele-specific primer extension and analysis by MALDI-TOF MS. Initial evaluation of the assays was performed using genomic DNA. Multiplexes were also evaluated from artificial mixtures to establish sensitivity and precision of the semi-quantitative readout of SNP alleles. Final performance was established using cell-free fetal DNA from maternal plasma.

Extraction of cell-free fetal DNA was performed using a modified Qiagen MinElute protocol.

Two multiplex reactions were developed that cumulatively integrated the detection of RhD exons 4, 5, 7, 10 and the detection of the RhD psi pseudogene conversion with 16 high-frequent SNPs. The use of 16 SNPs statistically provides up to 4 assays, which can confirm the presence of fetal DNA through detection of the paternally-inherited fetal allele. Performance of the multiplexed assays in artificial mixtures and in cell-free fetal DNA extracted from maternal plasma was demonstrated.

The method comprises the following 8 steps:

1. Isolate plasma and peripheral blood mononuclear cells (PBMC) from whole blood.

2. Purify cell-free DNA from the plasma (designated fetal DNA).

3. Purify DNA from PBMC (designated maternal DNA).

4. Prepare fetal and maternal DNA working dilutions (0.15 ng/μl).

5. Amplify the fetal and maternal DNA.

6. Process the Iplex™ Gold extend reactions on the amplified fetal and maternal DNA.

7. Dispense the MassExtend reaction products to a SpectroCH IP® array.

8. Analyze samples on the MassARRAY Analyzer Compact.

9. Interpret the results using with the aid of Table 1.

TABLE 1 RhD Test Interpretation Test RhD/ RhD/ RhD RhD Inter- RhD psi RhD psi RhD Exon Exon pre- Exon 4 Exon 4 Exon 5 7 10 tation Gene deletion C G C C — RhD− Gene conversion C G C C T RhD− RhD-CE-D; exons 1 and 10 of RhD gene present Gene conversion C G C C T RhD− RhD-CE-D; exons 1-3 and 9-10 of RhD gene present Pseudogene RhDy AT A G T T RhD− homozygous Pseudogene RhDy AT AG G T T RhD+ heterzygous Apparently intact A G G T T RhD+ RhD gene; possibly bearing single point mutations RhCE alleles denoted in bold and underlined represent leakage from allele-specific priming. Any negative result is a true negative. Any positive result is a true positive. Inconclusive results will result in further testing and/or therapy.

Step 5 and 6 are further described herein. Following genomic amplification, the assay interrogates amplified regions through the use of specific primers that are designed to hybridize directly adjacent to the site of interest. These DNA oligonucleotides are referred to as iPLEX MassEXTEND primers. In the extension reaction, the iPLEX primers are hybridized to the complementary DNA templates and extended with a DNA polymerase. Special termination mixtures that contain different combinations of deoxy- and dideoxynucleotide triphosphates along with enzyme and buffer, direct limited extension of the iPLEX primers. Primer extension occurs until a complementary dideoxynucleotide is incorporated.

The extension reaction generates primer products of varying length, each with a unique molecular weight. As a result, the primer extension products can be simultaneously separated and detected using Matrix Assisted Laser Desorption/Ionization, Time-Of-Flight(MALDI-TOF) mass spectrometry on the MassARRAY® Analyzer Compact. Following this separation and detection, SEQUENOM's proprietary software automatically analyzes the data and presents the assay results in the BioReporter RhD report.

A more specific protocol is provided in the Tables below. These conditions are not intended to limit the scope of the invention.

TABLE A PCR Master Mix Preparation (MMX) Final Conc. Volume Volume per 50 μl per each per 100 MMX Reagent rxn 50 μl (ul) rxn (ul) MMX1 Water N/A 7.55 755 10×PCR Buffer (contains 1.25x 6.25 625 15 mM MgCl2, Tris-Cl, KCl, (NH4)2SO4, pH 8.7 (Qiagen) 25 mM MgCl₂ 1.625 mM 3.25 325 (Qiagen) PCR Nucleotide Mix 800 μM 1 100 (10 mM each dATP, dCTP, (200 uM dGTP, dUTP) (Roche) each) 2 U/μl Uracil-DNA- 2.5 U/rxn 1.25 125 Glycosylase (UDG)(NEB) 5 U/μl HotStar Taq 3.5 U/rxn 0.7 70 (Qiagen) Sub Total for MMX1 20 2000 MMX2 0.5-1.5 uM RhD primers 0.1-0.5 uM 10 1000 Mix (Operon/IDT) each MMX Total for MMX 30 3000 Sample DNA ng/ul 20 PCR Reaction Total 50

1.2.1 Combine 20 ul of MMX1 and 10 ul of MMX2 to make 30 ul of each PCR MMX.

1.2.2 Add 20 ul of sample (plasma DNA) to MMX

1.2.3 Mix well, seal plate, spin briefly and cycle according to following parameters in table 3.

TABLE B PCR 30-11Cycling Conditions (two steps cycling) Temp. Time Cycles Notes 30 C. 10 min  1 UDG Incubation 94 C. 15 min  1 Initial Denaturation 94 C. 20 sec Target Amplification 56 C. 30 sec {close oversize brace} 30 cycles 72 C.  1 min 94 C. 20 sec Product Amplification 62 C. 30 sec {close oversize brace} 11 cycles 72 C.  1 min 72 C.  3 min  1 Final Extension  4 C. Forever  1 Hold

1.2.4 10 uL PCR Aliquots

Prepare two iPLEX EXTEND reaction plates by plating 10 uL PCR samples from each well of the PCR plate into two new 96-well plates designated for SAP and EXTEND reactions using the liquid handler

1.3 SAP Reaction

1.3.1 Prepare the SAP mixes according to Table 4 below. Dispense 6 μA SAP mix to the corresponding wells of one V-bottom Sarstedt 96-well plate. Transfer 4 μl SAP from the 96-well stock plate to each of the 96-well PCR plates, using a Liquid Handler.

TABLE C SAP Cocktail preparation Volume [uL] (60% overhang) Reagent Final C n = 1 160 Lot# Nanopure Water, n/a 2.95 472 Autoclaved SAP Buffer, 10× 0.85x 0.34 54.4 SAP (1.7 U/ul = 1.2 U/rxn 0.71 113.6 transparent label) Total volume [uL] n/a 4 640 n/a

1.3.2 When preparation is finished, seal the plate, vortex, centrifuge briefly and cycle each plate according to the following parameters in the table below.

TABLE D SAP Thermal Cycling Conditions Temperature Incubation Time Plate ID 37° C. 40 minutes Program ID: SAP-40-5 80° C.  5 minutes  4° C. store 1.4 iPLEX Extension

TABLE E iPLEX EXTEND Cocktail Mix Preparation Volume [uL] Volume = 1 − (60% Extend Reagent Rxn overhang) 160 Water (HPLC grade) 1.238 198.08 iPLEX detergent free 0.4 64 buffer (10×) iPLEX Termination 0.4 64 Mix Extend Primer Mix 1.88 300.8 Thermosequenase 0.082 13.12 (32 U/uL) Total Volume 4 640

-   -   1.4.1 Add 6 ul cocktail to each well of one V-bottom Sarstedt 96         plate. Transfer 4 μl iPLEX-EXTEND cocktail from the V-bottom         Sarstedt 96 plate to each well of the 96-SAP/PCR plates, using a         Matrix MassARRAY Liquid Handler into well positions according to         plate lay out.     -   1.4.2 Seal the plates, vortex, centrifuge briefly and cycle         according to the parameters listed below in Table 10.

TABLE F hME-100 Incubation Temperature Time Cycles Notes 94° C. 2 minutes 1 Plate ID: 1) 06-28-2006_HLBK_ST_DOL 94° C. 5 seconds 99 cycles Program ID: hME-100 52° C. 5 seconds Cycler ID: BLK0116, BSE 0046 72° C. 5 seconds Cycler Bonnet ID (iM applicable):  4° C. forever 1

Example 2 Fetal Identifiers, Sex Test and Copy Number Determination

Selection of SNPs

Analysis of paternally-inherited alleles in clinical samples and correlation with Y-chromosome frequency in male fetuses was performed with a total of 16 SNPs; SNP assays for analysis of clinical samples were multiplexed as 8-plexes; all SNPs had a minor allele frequency (maf) of ˜0.4 in all ethnic groups and were unlinked.

For performance evaluation of a universal Fetal Identifier panel that can be multiplexed with disease-specific markers, a new panel of 87 NT SNPs with a pan-ethnic maf >0.4 was selected and multiplexed into 16-plexes.

Method of SNP Analysis

Analysis of SNPs in maternal buffy coat and maternal plasma was performed using the iPLEX™ assay and MassARRAY® technology (Jurinke, C., Oeth, P., van den Boom, D., MALDI-TOF mass spectrometry: a versatile tool for high-performance DNA analysis. Mol. Biotechnol. 26, 147-164 (2004); and Oeth, P. et al., iPLEX™ Assay: Increased Plexing Efficiency and Flexibility for MassARRAY® System through single base primer extension with mass-modified Terminators. SEQUENOM Application Note (2005), both of which are hereby incorporated by reference). In brief, the target region surrounding the SNP is first amplified by PCR. Subsequently an oligonucleotide primer is annealed to the PCR product and is extended allele-specifically by a single nucleotide using a mixture of 4 terminator nucleotides and a DNA polymerase. The extension products are transferred to a miniaturized chip array and are analyzed by MALDI-TOF Mass Spectrometry. Determination of the molecular mass of extension products allows unambiguous identification of the SNP allele present in the sample. The peak area ratio of mass signals allows the estimation of the relative abundance of the alleles in a given sample. FIG. 6 provides an overview of the assay used for SNP analysis.

Clinical Samples

The total sample set consisted of 35 paired blood/plasma samples from pregnant Caucasian woman (nine 1st trimester; twelve 2nd trimester; fourteen 3rd trimester).

The subset of samples used for correlation of Y-chromosome frequency and paternally-inherited alleles in maternal plasma consisted of 19 samples of pregnant Caucasian woman carrying a male fetus.

DNA Extraction

DNA extraction was performed from 1 ml of maternal plasma using the Qiagen MinElute kit for fetal genotyping.

DNA extraction from frozen blood (minus plasma) was performed from 4 ml using Qiagen's PureGene kit for maternal genotyping.

Results

An assay targeting sequence differences in the Amelogenin region on the X and Y chromosome was used to assess the relative amount of fetal DNA extracted from plasma of pregnant woman carrying a male fetus. Details of the AMG assay are depicted in FIGS. 3A-3C. X and Y-specific sequences can be discriminated by sequence specific iPLEX extension products and their respective mass signals. The peak area ratio of the extension products allows estimation of the relative amount of fetal DNA, because the Y-specific sequences represent 50% of the total fetal DNA contribution.

Sixteen of nineteen (84%) plasma samples with a male fetus showed a Y-chromosome frequency of higher than 5%, indicating presence of at least 10% fetal DNA in the extracted DNA.

FIG. 8 depicts typical performance results for a qualified fetal identifier. Here the ability of the SNP assay to estimate the quantity of fetal DNA in the background of maternal DNA was verified for a total of 1700 copies and a total of 170 copies using genomic DNA mixtures. Note that the standard deviation of the estimate of fetal DNA increases due to the significant influence of the sampling error at low copy numbers

Table 2 provides a list of SNPs that were multiplexed at 10+ plexing level and passed all phases of the validation shown in FIG. 7. Application of this assay panel to a model system for the detection of fetal DNA in maternal background showed that paternally-inherited fetal alleles can be detected with a sensitivity of 95% at 100% specificity if the sample preparation method can enrich the relative amount of fetal DNA to 20%. In Table 2, the minor allele frequency (MAF) for each SNP from different ethnic populations is provided. The ethnic populations are defined by the HapMap Project, where CEU represents individuals of Northern and Western Europe descent, HCB represents Han Chinese in Beijing, JAP represents Japanese in Tokyo, and YR1 represents the Yoruba in Ibadan, Nigeria.

TABLE 2 MAF MAF MAF MAF SNP CEU HCB JAP YRI rs11166512 0.43 0.41 0.50 0.49 rs11184494 0.50 0.40 0.48 0.50 rs11247894 0.43 0.39 0.32 0.44 rs12089156 0.46 0.49 0.44 0.43 rs12125888 0.40 0.43 0.48 0.43 rs12136370 0.42 0.48 0.42 0.48 rs12143315 0.40 0.42 0.42 0.42 rs12759642 0.39 0.48 0.48 0.42 rs156988 0.46 0.40 0.45 0.41 rs2050927 0.44 0.50 0.41 0.49 rs213624 0.48 0.44 0.40 0.34 rs2454175 0.46 0.48 0.43 0.40 rs4329520 0.45 0.43 0.40 0.44 rs4487973 0.47 0.43 0.44 0.40 rs454782 0.48 0.40 0.41 0.46 rs4648888 0.33 0.30 0.33 0.46 rs635364 0.49 0.40 0.46 0.43 rs660279 0.41 0.49 0.50 0.39 rs6687785 0.48 0.46 0.48 0.44 rs7551188 0.46 0.49 0.45 0.46 rs9431593 0.41 0.43 0.49 0.40

A multiplexed panel of 16 SNPs was analyzed with maf >0.3 in the same maternal plasma DNA extraction and established a baseline of maternal genotypes by analyzing DNA from PBMCs. Using the maternal genotype information, paternally-inherited alleles were identified in plasma samples and estimated the amount of fetal DNA from the peak area ratio of extension products representing paternally-inherited fetal alleles and maternal alleles.

The AMG XY frequency was then compared with the allele-frequency of paternally-inherited fetal alleles in informative SNPs. This comparison revealed that samples with a positive Y-frequency of 10% (used as a Limit-of-quantitation threshold) or more have significantly higher differences between maternally and paternally-inherited fetal allele-frequencies (p-value <0.001; Fishers' exact test). This data shows that Fetal Identifiers can be used as a non-gender specific approach for identification of the presence of fetal DNA. FIG. 8 exemplifies those results.

Example 3 Multiplex Schemes

The above described RhD, fetal identifier and sex test may be run simultaneously in various multiplex schemes. Exemplary multiplex schemes are provided in FIG. 10. For example, in the Scenario 1 assay, two multiplex reactions are run in parallel. In the MP1, the following reactions are performed: 10 Fetal Identifiers reactions, the RhD 4 reaction, the RhD 10 reaction and the SRY reaction. In the MP2, the following reactions are performed: 11 Fetal Identifiers reactions, the RhD 4 psi quantitative reaction, the RhD 5 reaction and the RhD 7 reaction. Other exemplary multiplex schemes are provided in FIG. 10, but are not intended to limit the scope of the invention.

The PCR primers and extend primers for MP1 and MP2 are provided below in Table 3. Lower case nucleotides in the extend primer sequence represent non-template nucleotides that are added as mass modifiers. Additional fetal identifiers which may be used as described herein are provided in Table 4.

TABLE 3 Multiplex Primer Name Amplification primer Amplification primer Extend Primer sequence MP1 RhD-10-3r-i ACGTTGGATGACGCTCATGA ACGTTGGATGAACTCCATTT gGTCTCCAATGTTCGCGCAGGCAC CAGCAAAGTC TCTCTGACTC (SEQ ID NO: 15) (SEQ ID NO: 12) (SEQ ID NO: 13) MP1 RhD-4-3r-i ACGTTGGATGCTGCCAAAGC ACGTTGGATGTGGCAGACAA GAACGGAGGATAAAGATCAGA CTCTACACG ACTGGGTGTC (SEQ ID NO: 17) (SEQ ID NO: 1) (SEQ ID NO: 2) MP1 rs7551188 ACGTTGGATGATCCCTGGTT ACGTTGGATGGAGCCTCTCA GGACAGATTCTGGGAC CCTTCCTTAG GTGTCTATAC (SEQ ID NO: 29) (SEQ ID NO: 27) (SEQ ID NO: 28) MP1 rs11247894 ACGTTGGATGATCCTAGATA ACGTTGGATGGGAGGAAAGA CCAAAGCCAAGAATTCA GCCCAAAGCC GAAGATTGTG (SEQ ID NO: 32) (SEQ ID NO: 30) (SEQ ID NO: 31) MP1 rs6687785 ACGTTGGATGATGCTGTAAA ACGTTGGATGTTCTCCTCTG CCTCAACAGTACACTTAATC GAGCCTCAAC ACCTGCTTTC (SEQ ID NO: 35) (SEQ ID NO: 33) (SEQ ID NO: 34) MP1 rs4487973 ACGTTGGATGTCAGAGAGTG ACGTTGGATGGAATGCATGC cAGGTCACACAGTTAGGATT ACAAGACCTG CAACTTAGGG (SEQ ID NO: 38) (SEQ ID NO: 36) (SEQ ID NO: 37) MP1 rs4648888 ACGTTGGATGCAGAGAGTCC ACGTTGGATGTGCCCAGACC aTGGACCTTCGGAAAGGATA CCTGTTATTG AGAGAGGTCA (SEQ ID NO: 41) (SEQ ID NO: 39) (SEQ ID NO: 40) MP1 rs12089156 ACGTTGGATGGCTACATACT ACGTTGGATGCCTGCTGGCA TACTATGTGGTCTCAACTATAT ATGTGGTCTC ACAAATCTTC (SEQ ID NO: 44) (SEQ ID NO: 42) (SEQ ID NO: 43) MP1 rs2050927 ACGTTGGATGTTCTAGCTTG ACGTTGGATGTTGGGTGCAG TGCTTCTCCTCCATCATCCTTAGC CTTCTCCTCC AGTAGTCATC (SEQ ID NO: 47) (SEQ ID NO: 45) (SEQ ID NO: 46) MP1 rs12125888 ACGTTGGATGCAACATCCTG ACGTTGGATGAGACAATTTC TACATGACTATCTCCTCCCTTAGGT TACATCACTC TGTCCTCTGG (SEQ ID NO: 50) (SEQ ID NO: 48) (SEQ ID NO: 49) MP1 rs12143315 ACGTTGGATGACAGGCATGA ACGTTGGATGTGCCATTGGT CCATCTTACCCAGCCTCTTTCTTCAA GCCATCTTAC ACAGTCACTC (SEQ ID NO: 53) (SEQ ID NO: 51) (SEQ ID NO: 52) MP1 rs213624 ACGTTGGATGTAGGTCAAGC ACGTTGGATGTGTCCACCCA gGCCAAGGCCTCGGAGTCTGAACAGTT CAAGGCCTC GGAGCAGCCA (SEQ ID NO: 56) (SEQ ID NO: 54) (SEQ ID NO: 55) MP1 SRY_5-ib ACGTTGGATGAGCATCTAGG ACGTTGGATGAGCAACGGGA cGTTACCCGATTGTCCTAC TAGGTCTTTG CCGCTACAG (SEQ ID NO: 57) (SEQ ID NO: 24) (SEQ ID NO: 25) MP2 RhD-4-psi- ACGTTGGATGGACTATCAGG ACGTTGGATGTGCGAACACG cTGCAGACAGACTACCACATGAAC 3r-i GCTTGCCCCG TAGATGTGAC (SEQ ID NO: 18) (SEQ ID NO: 5) (SEQ ID NO: 58) MP2 RhD-5_3r-i ACGTTGGATGAATCGAAAGG ACGTTGGATGCTGAGATGGC ATGCCGTGTTCAACACCTACTATGCT AAGAATGCCG TGTCACCACG (SEQ ID NO: 19) (SEQ ID NO: 7) (SEQ ID NO: 8) MP2 RhD-7-3r-i ACGTTGGATGAGCTCCATCA ACGTTGGATGTTGCCGGCTC CTTGCTGGGTCTGCTTGGAGAGATCA TGGGCTACAA CGACGGTATC (SEQ ID NO: 22) (SEQ ID NO: 9) (SEQ ID NO: 10) MP2 rs660279 ACGTTGGATGTTTCAGCAAC ACGTTGGATGTGCCCGTAAG CTTGATGTGCTTCCCTG CACTCTGAGC TAGGAGAGTG (SEQ ID NO: 61) (SEQ ID NO: 59) (SEQ ID NO: 60) MP2 rs635364 ACGTTGGATGGAAATTTCTG ACGTTGGATGAGAGACTCCA TGGATTACTGGCAAAGAC GATTACTGGC TTTGTTTGGG (SEQ ID NO: 64) (SEQ ID NO: 62) (SEQ ID NO: 63) MP2 rs9431593 ACGTTGGATGTTGAGATCAG ACGTTGGATGGCCTCAGTAG TGTTCCTGACTCTCAAAAT TGTCGGTTCC TCACATAAGG (SEQ ID NO: 67) (SEQ ID NO: 65) (SEQ ID NO: 66) MP2 rs11166512 ACGTTGGATGCTTCATCCAC ACGTTGGATGTGACCAGATG CCACTATATCCACCTTTTCT TATATCCACC TTGGATTAG (SEQ ID NO: 70) (SEQ ID NO: 68) (SEQ ID NO: 69) MP2 rs4329520 ACGTTGGATGGAAAGTTGTC ACGTTGGATGATGTCCACCT GCGTGGTTCTAGACTTATGC GTGGTAGAGG CCTGCTCCAC (SEQ ID NO: 73) (SEQ ID NO: 71) (SEQ ID NO: 72) MP2 rs454782 ACGTTGGATGCTGTTAAGAT ACGTTGGATGCTGTCTTCCT AACTCCCATATTAGTCCACAG GCCAACTCCC CATTGCTCTG (SEQ ID NO: 76) (SEQ ID NO: 74) (SEQ ID NO: 75) MP2 rs12136370 ACGTTGGATGGAGTAGTTCT ACGTTGGATGCTCCTGGAAA gGCAGTAAGCTATTCTTGGGG TTGCAGTAAGC ACAGCAAAAG (SEQ ID NO: 79) (SEQ ID NO: 77) (SEQ ID NO: 78) MP2 rs12759642 ACGTTGGATGATTCTTCCTG ACGTTGGATGGGAAATACCA caTCGGGATTCCCTGAACAAAA GGACTCAGAC GCAACCACAG (SEQ ID NO: 82) (SEQ ID NO: 80) (SEQ ID NO: 81) MP2 rs11184494 ACGTTGGATGAGCTGGCCAT ACGTTGGATGGCCAATCTAT ATTTGACTTTCCTACTCCTTAAC GTTTATTTGAC GAAGAATTAC (SEQ ID NO: 85) (SEQ ID NO: 83) (SEQ ID NO: 84) MP2 rs2454175 ACGTTGGATGGGAATCAGAC ACGTTGGATGGCCCAGCAGG cCTTCAAGGATTGGAATTAGAGT CTGTAAACAC ACACTTTTAT (SEQ ID NO: 88) (SEQ ID NO: 86) (SEQ ID NO: 87) MP2 rs156988 ACGTTGGATGAAAGCTCTGT ACGTTGGATGGAAAGGGCTA tCGTCTCGGTCCTTCCTTTTCACTT GATGCGTCTC TGTAAGGAGG (SEQ ID NO: 91) (SEQ ID NO: 89) (SEQ ID NO: 90)

TABLE 4 Multiplex SNP_ID Amplification primer Amplification primer Extend Primer sequence W1 rs10793675 ACGTTGGATGAAGAGATGAG ACGTTGGATGCTCTGTATTT AACGGCTCAACAGTT ACAGACTGGG ATAGCTTTC (SEQ ID NO: 94) (SEQ ID NO: 92) (SEQ ID NO: 93) W1 rs1829309 ACGTTGGATGATCTCTGAGT ACGTTGGATGTTCCTAATCA TTGCTTTGGGGAGCAG TGACACCACC GGAGAGACCG (SEQ ID NO: 97) (SEQ ID NO: 95) (SEQ ID NO: 96) W1 rs6602279 ACGTTGGATGTTTCAGCAAC ACGTTGGATGTGCCCGTAAG CTTGATGTGCTTCCCTG CACTCTGAGC TAGGAGAGTG (SEQ ID NO: 61) (SEQ ID NO: 59) (SEQ ID NO: 60) W1 rs635364 ACGTTGGATGGAAATTTCTG ACGTTGGATGAGAGACTCCA TGGATTACTGGCAAAGAC GATTACTGGC TTTGTTTGGG (SEQ ID NO: 64) (SEQ ID NO: 62) (SEQ ID NO: 63) W1 rs9431593 ACGTTGGATGTTGAGATCAG ACGTTGGATGGCCTCAGTAG TGTTCCTGACTCTCAAAAT TGTCGGTTCC TCACATAAGG (SEQ ID NO: 67) (SEQ ID NO: 65) (SEQ ID NO: 66) W1 rs11166512 ACGTTGGATGCTTCATCCAC ACGTTGGATGTGACCAGATG CCACTATATCCACCTTTTCT TATATCCACC TTTGGATTAG (SEQ ID NO: 70) (SEQ ID NO: 68) (SEQ ID NO: 69) W1 rs4329520 ACGTTGGATGGAAAGTTGTC ACGTTGGATGATGTCCACCT GCGTGGTTCTAGACTTATGC GTGGTAGAGG CCTGCTCCAC (SEQ ID NO: 73) (SEQ ID NO: 71) (SEQ ID NO: 72) W1 rs454782 ACGTTGGATGCTGTTAAGAT ACGTTGGATGCTGTCTTCCT AACTCCCATATTAGTCCACAG GCCAACTCCC CATTGCTCTG (SEQ ID NO: 76) (SEQ ID NO: 74) (SEQ ID NO: 75) W1 rs12136370 ACGTTGGATGGAGTAGTTCT ACGTTGGATGCTCCTGGAAA gGCAGTAAGCTATTCTTGGGG TTGCAGTAAGC ACAGCAAAAG (SEQ ID NO: 79) (SEQ ID NO: 77) (SEQ ID NO: 76) W1 rs12759642 ACGTTGGATGATTCTTCCTG ACGTTGGATGGGAAATACCA caTCGGGATTCCCTGAACAAAA GGACTCAGAC GCAACCACAG (SEQ ID NO: 82) (SEQ ID NO: 80) (SEQ ID NO: 81) W1 rs11184494 ACGTTGGATGAGCTGGCCAT ACGTTGGATGGCCAATCTAT ATTTGACTTTCCTACTCCTTAAC GTTTATTTGAC GAAGAATTAC (SEQ ID NO: 85) (SEQ ID NO: 83) (SEQ ID NO: 84) W1 rs2454175 ACGTTGGATGGGAATCAGAC ACGTTGGATGGCCCAGCAGG cCTTCAAGGATTGGAATTAGAGT CTGTAAACAC ACACTTTTAT (SEQ ID NO: 88) (SEQ ID NO: 86) (SEQ ID NO: 87) W1 rs1452628 ACGTTGGATGGCTTGTGCTT ACGTTGGATGGGTCAAGCAA acatAGTTATTCCTAGGGCTTCTC TGTTGTGTGG AGGCTTCAAG (SEQ ID NO: 100) (SEQ ID NO: 98) (SEQ ID NO: 99) W1 rs156988 ACGTTGGATGAAAGCTCTGT ACGTTGGATGGAAAGGGCTA tCGTCTCGGTCCTTCCTTTTCACTT GATGCGTCTC TGTAAGGAGG (SEQ ID NO: 91) (SEQ ID NO: 89) (SEQ ID NO: 90) W1 rs4570430 ACGTTGGATGACCCGAGCCA ACGTTGGATGGCACATGGAG GGTATCATAAGATACCTATGATGTC ATCAGGTATC ATGAATGGTC (SEQ ID NO: 103) (SEQ ID NO: 101) (SEQ ID NO: 102) W1 rs12062414 ACGTTGGATGTGCGTCAACC ACGTTGGATGGGAAAGTCCT ggaaTTTCCAGTTCTATTCCAGCCTC TTTCCAGTTC CGACTGTTTG (SEQ ID NO: 106) (SEQ ID NO: 104) (SEQ ID NO: 105) W1 rs7545381 ACGTTGGATGCCAGTCAAGC ACGTTGGATGGTGAGCACAA tccCTGAATGACAAAAGGGGAAGATA TAAGGACAAA CTGTGTTCTA (SEQ ID NO: 109) (SEQ ID NO: 107) (SEQ ID NO: 108) W1 rs6427673 ACGTTGGATGGGACTAAAAC ACGTTGGATGGTCTCTCTAG ccctcGCCAAACTTAGACCAAGGACAAC AGGGCCAAAC TACTAGTAAC (SEQ ID NO: 112) (SEQ ID NO: 110) (SEQ ID NO: 111) W1 rs10802761 ACGTTGGATGTCTTCTAAAA ACGTTGGATGGGATGAGGTT AGTTATGAAATAAGTTTTATTCATTTAC TGTAGTTATG TTGACTAAGC (SEQ ID NO: 115) (SEQ ID NO: 113) (SEQ ID NO: 114) W2 rs642449 ACGTTGGATGCCAAAAAACC ACGTTGGATGAGATTGCCTC CCTCTGCCTCCCCTA ATGCCCTCTG TCCATGTGAC (SEQ ID NO: 118) (SEQ ID NO: 116) (SEQ ID NO: 117) W2 rs4839419 ACGTTGGATGCTGCCGCATC ACGTTGGATGATGTGTTTGT CCTTCACAAAGCCGA CCTTCACAA GGCCACTTCC (SEQ ID NO: 121) (SEQ ID NO: 119) (SEQ ID NO: 120) W2 rs9324198 ACGTTGGATGAAAGGCCTAC ACGTTGGATGCAAAATATGT cGTTTGCTGGAAGCCT TGTTTGCTGG GTGAATCAGC (SEQ ID NO: 124) (SEQ ID NO: 122) (SEQ ID NO: 123) W2 rs1192619 ACGTTGGATGGCTCAACTCT ACGTTGGATGCCAGGAATGG TGGCCAGAAGAAGGAG GAACCAATCG GCATGTGTTC (SEQ ID NO: 127) (SEQ ID NO: 125) (SEQ ID NO: 126) W2 rs4657868 ACGTTGGATGCTAACCAGGA ACGTTGGATGCTAGCGTACC AGACACCCCCATACATTA AAAGACACCC CAATGGAATC (SEQ ID NO: 130) (SEQ ID NO: 128) (SEQ ID NO: 129) W2 rs6426873 ACGTTGGATGTAAATCAGGG ACGTTGGATGAAGTGCTAGG cccCTGCCTTCTCTTCCAA CTGCCTTCTC GTTACAGGTG (SEQ ID NO: 133) (SEQ ID NO: 131) (SEQ ID NO: 132) W2 rs438981 ACGTTGGATGTGTGCAAATT ACGTTGGATGGAACATTGGT ATGGACCACAAAAAACTTA GGCTAACAT ATTTAAACTC (SEQ ID NO: 136) (SEQ ID NO: 134) (SEQ ID NO: 135) W2 rs12125888 ACGTTGGATGAGACAATTTC ACGTTGGATGCAACATCCTG TCTGTCCTCTGGTATCCTCT TGTCCTCTGG TACATCACTC (SEQ ID NO: 137) (SEQ ID NO: 49) (SEQ ID NO: 48) W2 rs3128688 ACGTTGGATGATCAAGAGGA ACGTTGGATGGATTTACTCA cAAAATGGACAGAAGTTGAA AAATGGACAG ACTCTCTGGG (SEQ ID NO: 140) (SEQ ID NO: 138) (SEQ ID NO: 139) W2 rs4987351 ACGTTGGATGGTGCATGGGC ACGTTGGATGCCAAACAGGG gCATCTAGACACATTTTGTGC TCATCTAGAC CCAATGGTAG (SEQ ID NO: 143) (SEQ ID NO: 141) (SEQ ID NO: 142) W2 rs6692911 ACGTTGGATGCTATTCCCTC ACGTTGGATGATTAAGATGG tccAAGAGCATTTTTCCTCTTC CTCAAAGAGC GTAGTTAAG (SEQ ID NO: 146) (SEQ ID NO: 144) (SEQ ID NO: 145) W2 rs6684679 ACGTTGGATGTATGTTACTT ACGTTGGATGTCTTAAGGTG ggaCCACTGAGGAGATACACTA GCCTTGGCCC TCTCCCTCTG (SEQ ID NO: 149) (SEQ ID NO: 147) (SEQ ID NO: 148) W2 rs4320829 ACGTTGGATGGGTTCTATGG ACGTTGGATGTGCTAGACAC ggtcACCTCTTTTCATAACAGGA CTTTGGTGAG TTTAACTGCC (SEQ ID NO: 152) (SEQ ID NO: 150) (SEQ ID NO: 151) W2 rs4658481 ACGTTGGATGCTGCTAAGCA ACGTTGGATGGTGGTAGAAA atacGCATGAGAGAAAGGGAAAG TGAGAGAAAG CAAATGTCAGC (SEQ ID NO: 155) (SEQ ID NO: 153) (SEQ ID NO: 154) W2 rs3768458 ACGTTGGATGCCAAATGTCT ACGTTGGATGGAGTTTATGT CTTAGTTACAAAGAAAATTGTGAG TAGTTACAAAG AATGTCAAC (SEQ ID NO: 158) (SEQ ID NO: 156) (SEQ ID NO: 157) W2 rs860954 ACGTTGGATGTAGCCTTTAG ACGTTGGATGCCATTCTTGT TCTTGATGCCTTACAAAATAAATAT TCTTGATGCC ATGTTTTGTC (SEQ ID NO: 161) (SEQ ID NO: 159) (SEQ ID NO: 160) W2 rs10453878 ACGTTGGATGGAGGAGCTAA ACGTTGGATGGGGATATGAA AAACAAATCCTCCTTTCTTTTAATTC CAAGTAGGAC TTACAACAGAG (SEQ ID NO: 164) (SEQ ID NO: 162) (SEQ ID NO: 163) W2 rs10753912 ACGTTGGATGGAGATTATAT ACGTTGGATGATTCTTCTAA GAGATTATATGTCTCTTTAATATTGTC GTCTCTTTAA CTTTTAGGC (SEQ ID NO: 167) (SEQ ID NO: 165) (SEQ ID NO: 166) W2 rs1637944 ACGTTGGATGCTAATGCCTC ACGTTGGATGAATAGCAAAC cccccATATCATTTGCAATTGCATGGTT CTTTTCTTCC AACAGGTGGG (SEQ ID NO: 170) (SEQ ID NO: 168) (SEQ ID NO: 169) W2 rs4839282 ACGTTGGATGGAATCCTGGC ACGTTGGATGTGGGTTCACA gatgTCTCTTAAAGAGCAAAAAGCTAAG AGCTCATTAG TGAGTCTTGC (SEQ ID NO: 173) (SEQ ID NO: 171) (SEQ ID NO: 172)

Multiplex scheme 3 in FIG. 10 includes an albumin assay which may be performed to determine total copy number of DNA molecules for the human serum albumin gene. The albumin assay is useful to measure how much DNA is loaded into a particular reaction. It acts as an internal control and a guide to the likelihood of success for a particular PCR reaction. For example, if only 400 copies of ALB are measured then the probability of detecting any fetal DNA is very low. Primers for the Albumin assay are provided in FIG. 4.

The entirety of each patent, patent application, publication and document referenced herein hereby is incorporated by reference. Citation of the above patents, patent applications, publications and documents is not an admission that any of the foregoing is pertinent prior art, nor does it constitute any admission as to the contents or date of these publications or documents.

Modifications may be made to the foregoing without departing from the basic aspects of the invention. Although the invention has been described in substantial detail with reference to one or more specific embodiments, those of ordinary skill in the art will recognize that changes may be made to the embodiments specifically disclosed in this application, yet these modifications and improvements are within the scope and spirit of the invention.

The invention illustratively described herein suitably may be practiced in the absence of any element(s) not specifically disclosed herein. Thus, for example, in each instance herein any of the terms “comprising,” “consisting essentially of,” and “consisting of” may be replaced with either of the other two terms. The terms and expressions which have been employed are used as terms of description and not of limitation, and use of such terms and expressions do not exclude any equivalents of the features shown and described or portions thereof, and various modifications are possible within the scope of the invention claimed. The term “a” or “an” can refer to one of or a plurality of the elements it modifies (e.g., “a reagent” can mean one or more reagents) unless it is contextually clear either one of the elements or more than one of the elements is described. The term “about” as used herein refers to a value within 10% of the underlying parameter (i.e., plus or minus 10%), and use of the term “about” at the beginning of a string of values modifies each of the values (i.e., “about 1, 2 and 3” is about 1, about 2 and about 3). For example, a weight of “about 100 grams” can include weights between 90 grams and 110 grams. Thus, it should be understood that although the present invention has been specifically disclosed by representative embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and such modifications and variations are considered within the scope of this invention.

Embodiments of the invention are set forth in the claims that follow. 

What is claimed is:
 1. A method for determining the relative amount of fetal nucleic acid in a maternal plasma sample, comprising: (a) amplifying at least 10 polymorphic sites in nucleic acid obtained from a maternal plasma sample, which polymorphic sites comprise single nucleotide polymorphisms with a minor allele frequency of greater than 0.3 and are selected from the group consisting of: rs7551188, rs11247894, rs6687785, rs4487973, rs4648888, rs12089156, rs2050927, rs12125888, rs12143315, rs213624, rs660279, rs635364, rs9431593, rs11166512, rs4329520, rs454782, rs12136370, rs12759642, rs11184494, rs2454175, rs156988, rs10793675, rs1829309, rs1452628, rs4570430, rs12062414, rs7545381, rs6427673, rs10802761, rs642449, rs4839419, rs9324198, rs1192619, rs4657868, rs6426873, rs438981, rs3128688, rs4987351, rs6692911, rs6684679, rs4320829, rs4658481, rs3768458, rs860954, rs10453878, rs10753912, rs1637944 and rs4839282; (b) quantifying the relative amount of the alleles at said at least 10 polymorphic sites; and (c) expressing the relative amounts of fetal and maternal alleles as a ratio, wherein the ratio indicates the relative amount of fetal nucleic acid present in the maternal sample.
 2. The method of claim 1, wherein said at least 10 polymorphic sites are selected from the group consisting of rs7551188, rs11247894, rs6687785, rs4487973, rs4648888, rs12089156, rs2050927, rs12125888, rs12143315, rs213624, rs660279, rs635364, rs9431593, rs11166512, rs4329520, rs454782, rs12136370, rs12759642, rs11184494, rs2454175 and rs156988. 